Field of the Invention
An exemplary embodiment of the present invention relates to an electric CVVT. More particularly, the present invention relates to a noise reducing structure of a speed reduction device that changes a rotation phase difference with respect to a sprocket by transmitting output shaft rotation of the electric motor to a camshaft.
Description of Related Art
In general, a continuously variable valve timing apparatus (CVVT. continuous variable valve timing, or Camshaft phaser) refers to an apparatus that controls valve operation timing of an engine.
A typical variable timing apparatus usually in a vehicle maker is a vane-type variable valve timing apparatus that occupies a relatively small space and is inexpensive.
However, such a vane-type variable valve timing apparatus cannot provide a prompt and accurate response when an oil pressure is low because an engine of the apparatus uses lubrication oil.
In particular, when the engine is in an idle state, in a high-temperature state, or in a start-up state, that is, when the engine oil pressure is insufficient, a phase of the camshaft cannot be relatively changed and an exhaust gas may be excessively discharged.
To supplement such a drawback, a study on an electric CVVT that can electrically control the valve timing with an electric motor has been activated.
For example, the electric CVVT is formed by arranging a camshaft driving a valve of an engine and a sprocket receiving a rotation force from the engine and rotatably driving the camshaft in a coaxial direction for enabling relative rotation, and may transmit rotation of the electric motor to the camshaft through a speed reduction device.
Such an electric CVVT changes a rotation phase with respect to the sprocket by transmitting rotation of an output shaft of the electric motor to the camshaft through the speed reduction device, and changes opening/closing timing of the engine valve.
Here, in the speed reduction device, an inner tooth portion opposing an external wheel of a ball bearing is provided in an interior diameter surface of a housing that is integrated with the sprocket and a plurality of rollers are arranged between an inner tooth and the external wheel of the ball bearing through a cage.
However, in such a speed reduction device, a backlash exists between the rollers and the cage and between the rollers and the inner tooth so that an excessive noise is generated from impact between the rollers and the cage and between the rollers and the inner tooth due to change in a torque of the camshaft.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.